Photographs by Craig Jones. From Grafton Flyford path from the Church. Fields were full of clover

The Clouded Yellow (Colias croceus) is one of the UK’s most charismatic migrant butterflies—fast-flying, golden-yellow, and often a thrilling surprise for observers in late summer. I’ve found some great images to show you what it looks like, and they should be appearing now.

🇬🇧 UK Presence and Ecology

• Migration: This species migrates from southern Europe and North Africa, typically arriving from May to November.
• Distribution: Most frequent in southern England, especially on chalk grasslands, but can turn up almost anywhere in good years.
• Habitat: Prefers open, sunny areas—coastal cliffs, downland, and fields with clovers and bird’s-foot trefoil.
• Breeding: Although it breeds in the UK, it rarely survives the winter, except in unusually mild microclimates like Bournemouth Undercliff.

🌦️ Clouded Yellow Years

In some years, mass migrations occur—these are fondly remembered as “Clouded Yellow Years,” when thousands may be seen across the countryside.

🔍 Identification Tips

• Upperwings: Bright yellow-orange with bold black borders.
• Underside: Yellow-green with two silver-white spots on the hindwings.
• Flight: Rapid and erratic, often mistaken for whites until you catch the golden flash.

If you’re planning habitat work or community surveys, this species is a great candidate for seasonal monitoring—especially in warm summers. Want help drafting a volunteer ID guide or adding it to your seasonal calendar?

The lifecycle of the Clouded Yellow (Colias croceus) is fascinating—especially because it’s shaped by its migratory nature and the UK’s climate. Here’s a breakdown of its stages and seasonal dynamics:

🥚 Egg Stage

• Timing: Eggs are laid from late spring through autumn, depending on arrival time.
• Location: Females lay eggs singly on host plants like clovers, lucerne, and bird’s-foot trefoil.
• Duration: Eggs hatch in about 5–10 days, depending on temperature.

🐛 Larval Stage (Caterpillar)

• Appearance: Green with pale lines, well-camouflaged among foliage.
• Feeding: Larvae feed on the leaves of their host plants, often low to the ground.
• Growth: Goes through several instars over 2–3 weeks, though cooler weather can slow development.

🐚 Pupal Stage (Chrysalis)

• Form: Pale green or yellowish chrysalis, attached to stems or leaves.
• Duration: Typically lasts 1–2 weeks, but vulnerable to damp and frost.
• Overwintering: Rare in the UK—most pupae perish in winter conditions, though some survive in mild microclimates.

🦋 Adult Stage

• Emergence: Adults emerge from May to November, with peak numbers in late summer and early autumn.
• Generations: In warm years, the Clouded Yellow can produce up to three broods in the UK.
• Behaviour: Adults are strong fliers, often seen darting across open landscapes. They feed on nectar from thistles, knapweed, and clovers.

🌍 Migratory Influence

• Origin: Most UK individuals are immigrants from southern Europe and North Africa.
• Breeding: Many breed successfully in southern England, but the species is not reliably resident due to winter mortality.
• Climate Sensitivity: Warmer years may allow more successful breeding and even overwintering, hinting at potential range expansion with climate change.